Taiwanese Patent No. I486550 provides a conventional optical interferometric apparatus for real-time full-field thickness inspection using angular incidence interferometry. The conventional optical interferometric apparatus includes a light source, a screen, an image acquisition unit and an image processing module. The light source radiates a spherical-wave front light beam on an object to be measured at an oblique angle, an interference fringe pattern (IFP) is imaged on the screen, the image acquisition unit captures the IFP on the screen and converts the image into a digital image, and the image processing module analyzes the digital image of the IFP to obtain a full-field thickness distribution of the object. However, the conventional optical interferometric apparatus cannot directly obtain the full-field thickness distribution of the object, and needs additional input of an average thickness of the object or an absolute thickness at one point of the object for calculating the full-field thickness distribution. Namely, additional time and measuring instruments (e.g., an instrument for measuring the absolute thickness) are required on the calculation of the full-field thickness distribution of the object.